The 2-aminopyridine-2-pyridone (2AP-2PY) dimer is linked by N-H···O=C and N-H···N hydrogen bonds, providing a model for the Watson-Crick hydrogen bond configuration of the adenine-thymine and adenine-uracil nucleobase pairs. Mass-specific infrared (IR) spectra of 2AP-2PY and its seven N-H deuterated isotopomers have been measured between 2550 and 3650 cm^-1 by IR laser depletion combined with UV two-color resonant two-photon ionization. The 2PY amide N-H stretch is a very intense band spread over the range 2700-3000 cm^-1 due to large anharmonic couplings. It is shifted to lower frequency by 710 cm^-1 or ~20% upon H-bonding to 2AP. On the 2AP moiety, the bound amino N-H stretch gives rise to a sharp band at 3140 cm^-1, which is downshifted by 354 cm^-1 or ~10% H-bonding to 2PY.

This work was carried out in the group of Prof. Samuel Leutwyler.

References:

• J. A. Frey, A. Müller, H.-M. Frey, S. Leutwyler;
  "Infrared depletion spectra of 2-aminopyridine·2-pyridone, a Watson Crick mimic of adenine·uracil"
  J. Chem. Phys., 121, 8237-8245, (2004); doi:10.1063/1.1795673.